dydt
  It's strange that this type of application would have a dc motor installed if its say less than 15 years old. Prior to the previous generation of VFDs reliabilty and service conditions generally meant you used a dc drive for varying speed. If its newer than that (say after 1980) then it may have been used for a reason. an example I can think of is low speed torque or starting  torque.
  AS some of the other guys have pointed out with vfd drives cooling is an issue if the motor has the fan on the shaft. I have on our site quit a few japanese (Toshiba) motors running at around the 40hz no problems. But I'm not sure about all brands of motor.

Keep us informed hey
Don

Ps      been intergrated lately or just derivated. (sorry couldn't resist that)

thanks for the reply don.

It will be a 120 V single phase in and  3 phase 220 V out to the motor. I want to keep the existing supply and avoid messing around with the wirings. I checked some suppliers and BALDOR is the only one I got. They have 1 phase in, 3 phase out for a VFC of up to 1 hp. Since AC motor is cheap I ordered 1 hp. I have to work around the surface speed and gear ratios. I want to run it as close to 60HZ as possible.

Thanks for the info. I will keep you posted.

best regards
dydt

Also, http://www.ab.com/drives/161/index.html for small 1-3ø drives.

cool, should be ok . will keep my fingers crossed
Don